Is it possible to set the viewport render maximum resolution when using Cycles?
There isn't really a way to do that yet. You can play with the Start Resolution under the render properties panel to force Cycles to start rendering at a lower resolution, however, it will still eventually progress to a full, retina-resolution render.

Although one could argue that because of the high resolution, it takes less sample iterations to get to a visually 'smooth' image (even though each sample iteration does take longer), so you can probably try lowering the Preview Samples count.